"Abel's sacrifice was accepted by God because it was made according to God's instructions. Cain, however, tried to approach God in his own way and was rejected by God (Genesis 4:3-5). From that point on, Cain became a symbol of those who try to approach God on their own terms."

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What brings us to perfection? An ingrained faith in God, the 'faith that makes real the things for which we hope' (Heb. 11:1), the faith whereby Abel offered to God a better sacrifice than Cain and was commended as righteous (cf. Heb 11:4). It is such faith that fills those assiduous in the search for truth with great aspiration for the exalted gifts of God, and leads them to the spiritual knowledge of created beings; and it pours into their hearts the inexhaustible treasures of the Spirit.

— Niketas Stethatos